Light emitting diodes with sensor segment for operational feedback

ABSTRACT

A light emitting device comprises a detector circuit and a light emitting diode (LED) die. The LED die includes a semiconductor stack grown on a substrate. The LED includes an emitter segment formed from one segment of the semiconductor stack. The LED die includes a photosensor segment formed from another segment of the semiconductor stack. The LED die includes a segmentation layer formed between the emitter segment and the photosensor segment. The segmentation layer electrically isolates the emitter segment from the photosensor segment. The LED die includes first electrodes configured to provide power to energize the emitter segment. The LED die includes second electrodes configured to send the current to the detector circuit. The detector circuit is configured to convert the current to a signal which provides operational feedback with respect to the emitter segment.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/272,776 filed on Feb. 11, 2019, which is a continuation of U.S.patent application Ser. No. 15/849,909 filed on Dec. 21, 2017, nowissued as U.S. Pat. No. 10,205,064, which claims the benefit of U.S.Provisional Application No. 62/438,357 filed on Dec. 22, 2017 andEuropean Application No. 17161812.7 filed on Mar. 20, 2017, the contentsof which are hereby incorporated by reference herein as if fully setforth.

FIELD OF INVENTION

This application is related to light emitting devices.

BACKGROUND

Photosensors provided proximate to a light emitting diode (LED) die areused to detect the light emissions from the LEDs on the die. Thephotosensors can be, for example, photodiodes or phototransistors. Thecurrent through the photosensor can then be used to detect a LED failureor be used in a feedback loop by a driver to drive the LED to achieve aconstant brightness level over time as the LED characteristics change.However, the photosensors must be properly and consistently positionedrelative to the LED die in order for the feedback signal to beconsistent from product to product. Moreover, the photosensors use realestate on the LED printed circuit board or other area. Furthermore, thephotosensors are sensitive to a broad range of light, including ambientlight, which affects the accuracy of the photosensors.

SUMMARY

Described herein are light emitting diodes (LEDs) having a sensorsegment for operational feedback. In general, the LED layers are formedor grown on a sapphire substrate, where the LED layers can be, forexample, Gallium nitride (GaN) layers. In an example, the LED emits bluelight. The LED layers are segmented, separated or isolated (collectivelyreferred to as “segmented” herein) to form at least two LED segments.One of the LED segments is used as a photosensor (referred to asphotosensor segment herein) with respect to the other LED segment(referred to as emitter segment herein). In an implementation,segmentation can be achieved by etching a trench. In anotherimplementation, segmentation can be achieved by forming, depositing orproviding an oxidation layer during LED layer growth. In animplementation, the photosensor may be structurally identical to theemitter segment but has a smaller footprint on the LED die. In animplementation, the photosensor segment alternates on a predeterminedbasis between functioning as a photosensor segment or as an emittersegment. Electrodes are provided on the LED die for all LED segments.The emitter segment is coupled in a conventional way to a power sourcefor energizing the emitter segment.

In an implementation, a small portion of the light from the emittersegment is transmitted sideways into the photosensor segment, which inturn generates a current. This current is generally proportional to thelight emitted by the emitter segment. The current may be used to detectthat the emitter segment is operating or may be used as a feedbacksignal to a driver. The driver uses the feedback signal to adjust thedrive current to create a constant light output from the emitter segmentover time or as it ages.

In an implementation, the light from the emitter segment is transmittedinto the sapphire substrate and due to internal reflection, reflectedback to the photosensor segment, which in turn generates a current whichcan be used as described herein.

In an implementation, the LED layers are segmented to form multiple LEDsegments, where each segment can represent a particular color. In thisimplementation, a red emitting segment can be used as the photosensorsegment as it has the smallest bandgap.

The photosensor segment is not significantly affected by incidentambient light since the photosensor segment is only sensitive to thenarrow emission wavelength of the emitter segment. Even if the emittersegment has an overlying phosphor layer that converts the primary lightto white light or another color, the emitter segment still emits itsprimary color light into the photosensor segment. Moreover, thephotosensor segment is always in the same position relative to theemitter segment. Therefore, the photosensor segment has greater accuracythan the conventional photosensors positioned proximate to an LED die.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 is an illustrative cross-sectional view of a single LED die,formed as a flip-chip, and a submount, where the LED layers aresegmented to form an emitting segment and a sensor segment for detectingthe emitter segment's light output in accordance with certainimplementations;

FIG. 2 is an illustrative bottom view of the LED die of FIG. 1 showingfour electrodes in accordance with certain implementations;

FIG. 3 is another illustrative bottom view of the LED die of FIG. 1showing four electrodes in accordance with certain implementations;

FIG. 4 is an illustrative schematic of the LED and sensor of FIG. 1 inaccordance with certain implementations;

FIG. 5 is an illustrative schematic of an operational feedback circuitin accordance with certain implementations;

FIG. 6 is an illustrative schematic of a circuit in accordance withcertain implementations;

FIG. 7 is yet another illustrative schematic of a circuit in accordancewith certain implementations;

FIG. 8 is an illustrative schematic for connecting multiple sensors onmultiple LED dies to a detector in accordance with certainimplementations;

FIG. 9 is an illustrative schematic of a circuit in accordance withcertain implementations;

FIG. 10 is yet another illustrative schematic of an operational feedbackcircuit in accordance with certain implementations;

FIG. 11 is another illustrative cross-sectional view of a single LED dieand a submount, where the LED layers are segmented to form an emittingsegment and a dual purpose emitter segment/sensor segment for detectingthe emitter segment's light output in accordance with certainimplementations;

FIG. 12 is another illustrative cross-sectional view of a single LED dieand a submount, where the LED layers are segmented to form an emittingsegment and a sensor segment for detecting the emitter segment's lightoutput in accordance with certain implementations; and

FIG. 13 is a flowchart for making LEDs with sensor segments inaccordance with certain implementations.

DETAILED DESCRIPTION

It is to be understood that the figures and descriptions for lightemitting diodes with sensor segments for operational feedback have beensimplified to illustrate elements that are relevant for a clearunderstanding, while eliminating, for the purpose of clarity, many otherelements found in typical device processing. Those of ordinary skill inthe art may recognize that other elements and/or steps are desirableand/or required in implementing the present invention. However, becausesuch elements and steps are well known in the art, and because they donot facilitate a better understanding of the present invention, adiscussion of such elements and steps is not provided herein.

FIG. 1 is an illustrative cross-sectional view of a LED die 100implemented in a flip-chip configuration, where all of the electrodesare on the bottom. In another implementation, a LED die can have one ormore electrodes on top and use wire bonds to create the electricalconnections. The LED die 100 is formed of semiconductor epitaxiallayers, including an n-type layer 105, an active layer 107, and a p-typelayer 109, grown on a growth substrate 110. The n-type layer 105, anactive layer 107, and a p-type layer 109 may be collectively referred toas a semiconductor stack. In a non-limiting illustrative example, thesemiconductor epitaxial layers are made from gallium nitride (GaN), theactive layer 107 emits blue light and the growth substrate 110 is atransparent sapphire substrate. The growth substrate 110 may remain orbe removed, such as by laser lift-off, etching, grinding, or by othertechniques. The growth processes are formed on a wafer scale and the LEDdies are then singulated from the wafer. A phosphor layer (not shown)may overlie the growth substrate 110 for converting the blue primarylight to white light or any other color light.

A metal electrode 119 electrically contacts the p-type layer 109, and ametal electrode 115 electrically contacts the n-type layer 105 via avertical conductor 117 through the p-type layer 109 and the active layer107. A thin dielectric (not shown) insulates the vertical conductor 117from the p-type layer 109 and the active layer 107. A dielectric layer120 insulates the metal electrode 115 from the p-type layer 109. In anon-limiting illustrative example, the electrodes 119 and 115 are goldpads that are ultrasonically welded to anode and cathode metal pads 129and 125 on a ceramic submount 130 or a printed circuit board. In animplementation, the ceramic submount 130 may have conductive vias (notshown) leading to bottom metal pads for bonding to a printed circuitboard.

During wafer processing of the LED dies 100, a surface is patterned andetched, using conventional techniques, to form a trench 135, whichelectrically isolates a photosensor segment 140 from an emitter segment150. The photosensor segment 140 functions as an embedded sensor in LEDdies 100. In an implementation, the trench 135 may be filled with atransparent material to improve the optical coupling between the emittersegment 150 and the photosensor segment 140. The photosensor segment 140has the exact same layers as the emitter segment 150 and has a verticalconductor 117 connecting its n-type layer 105 to a photosensor electrode145. The p-type layer 109 of the photosensor segment 140 is connected toa photosensor electrode 149. In an implementation, the photosensorsegment 140 will typically have an area that is less than 10% of theemitter segment 150. In an implementation, the photosensor segment 140may be a small portion along one edge of the emitter segment 150. Inanother implementation, the photosensor segment 140 may be surrounded bythe emitter segment 150. In another implementation, the photosensorsegment 140 may take up an entire edge of the LED die 100. The trench135 surrounds the photosensor segment 140 for complete electricalinsulation. In an implementation, electrical isolation may be providedby injection of certain types of atoms around the photosensor segment140, which causes the GaN material surrounding the photosensor segment140 to be effectively an insulator.

The photosensor electrodes 145 and 149 contact pads 155 and 159 on thesubmount 130 or printed circuit board for connection to a detectorcircuit (shown in FIGS. 4-10). In an implementation, there are fourelectrodes on the LED die 100 to allow the emitter segment 150 and thephotosensor segment 140 to be connected completely independently. FIG. 2illustrates a bottom view of the LED die 100 of FIG. 1. Electrodes 115and 119 and photosensor electrodes 149 and 145 are shown as strips. FIG.3 illustrates an alternative bottom electrode configuration showing theelectrodes 115 and 119 and photosensor electrodes 149 and 145 assquares. If the emitter segment 150 and the photosensor segment 140share a common reference, only three electrodes are needed.

Operationally, side light rays 160 emitted by the emitter segment 150impinges on the active layer 107 within the photosensor segment 140 andis converted into a small current in a direction opposite to the emittersegment 150 current. The current is the product of the photons excitingthe electrons in the photosensor segment's 140 active layer 107. Sincethe photosensor segment 140 and the emitter segment 150 have the sameactive layer 107, only the narrow wavelength of light emitted by emittersegment 150 is converted into a small current by the photosensor segment140. This is beneficial since ambient light will have little effect onthe output of the photosensor segment 140. Further, since thephotosensor segment 140 is very close to the emitter segment 150, thereis little light attenuation in the gap. Accordingly, the system is veryefficient, reproducible, and accurate. The vertical conductor 117 ispreferably located away from the emitter segment 150 to not attenuatethe light. A blue light ray 165 exiting the top of the emitter segment150 may be converted by a phosphor layer to any other color. Such aphosphor layer does not affect the operation of the photosensor segment140.

In an implementation where the substrate 110 is not removed, totallyinternally reflected and Fresnel reflected light rays 167 are reflectedback to the photosensor segment 1240 and are converted into a current ina direction opposite to the emitter segment 1250 current as describedherein.

FIG. 4 is an illustrative schematic of the LED die 100 showing theemitter segment 150 with electrodes 115 and 119 and the photosensorsegment 140 with photosensor electrodes 145 and 149. The direction offorward current I_(LED) into the emitter segment 150 to energize theemitter segment 150 is shown along with the current I_(S) beinggenerated by the photosensor segment 140 flowing in the oppositedirection.

FIG. 5 is an illustrative schematic of an operational feedback circuit500 in accordance with certain implementations. The operational feedbackcircuit 500 includes an emitter segment 505, a photosensor segment 510and a detector circuit 515 that is connected to the photosensor segment510. Although the photosensor segment 510 independently generates acurrent, a reverse bias voltage may be applied across it to operatephotosensor segment 510 in a linear range so that the photosensorsegment 510 output is proportional to the brightness of the emittersegment 505. Such an optional reverse bias voltage is not shown in thecircuit 500 for purposes of illustration.

The detector circuit 515 includes a transistor 520 connected toresistors R_(B), R_(C), and R_(E). An output voltage V_(out) isinversely related to the generated photosensor segment 510 current,which can be directly proportional to the brightness of the emittersegment 505. When there is little or no light, V_(out) will beapproximately V+. When the photosensor segment 510 current is large(V_(CE) of transistor 520 is negligible) the ratio of V_(out) to V+ isapproximately R_(E)/(R_(E)+R_(C))+V_(BE). Thus, V_(out) can be used todetect a fault with the emitter segment 505 or can be used as feedbackto a LED driver 530 to keep the brightness at the same level despite thecharacteristics of the emitter segment 505 changing over time. Since thephotosensor segment 510 output may be affected by temperature, atemperature compensation circuit may be added (not shown).

FIG. 6 is another illustrative schematic of a circuit 600 in accordancewith certain implementations. The circuit 600 includes an emittersegment 605, a photosensor segment 610 and a detector circuit 615 thatis connected to the photosensor segment 610. The detector circuit 615includes an operational amplifier 620 connected to a feedback resistorR_(FB). The output voltage V_(out) is equal to the photosensor segment615 current I_(S) multiplied by the feedback resistance, and has anegative magnitude. The feedback resistor R_(FB) can be chosen to adjustthe sensitivity of the output voltage V_(out) to the photosensor segment615 current I_(S). In this implementation, the photosensor segment 615is always biased at 0V and the bias does not change with changes in thephotosensor segment 615 current I_(S). If some other voltage bias isdesired, that bias should be applied to the “+” input terminal of theoperational amplifier 620. The output, V_(out), is inverted with respectto the sensor current I_(S).

FIG. 7 is another illustrative schematic of a circuit 700 in accordancewith certain implementations. The circuit 700 includes an emittersegment 705, a photosensor segment 710 and a detector circuit 715 thatis connected to the photosensor segment 710. The detector circuit 715includes an operational amplifier 720 connected to a feedback resistorR_(FB). The output voltage V_(out) is equal to the photosensor segment715 current I_(S) multiplied by the feedback resistance, and has anegative magnitude. The feedback resistor R_(FB) can be chosen to adjustthe sensitivity of the output voltage V_(out) to the photosensor segment715 current I_(S). In this implementation, the photosensor segment 715is always biased at 0V and the bias does not change with changes in thephotosensor segment 715 current I_(S). If some other voltage bias isdesired, that bias should be applied to the “+” input terminal of theoperational amplifier 720. At this point, the output, V_(out), isinverted with respect to the sensor current I_(S). The output, V_(out),is input to an inverting circuit 730 to un-invert V_(out). In animplementation, inverting circuit 730 is an operational amplifier 735.

FIG. 8 is an illustrative schematic of a circuit 800 for connectingmultiple sensors on multiple LED dies to a detector in accordance withcertain implementations. The circuit 800 includes multiple LED dies 805₁-805 _(N), each of which includes an emitter segment 810 ₁-810 _(N) anda photosensor segment 815 ₁-815 _(N). Each photosensor segment 815 ₁-815_(N) is connected to a detector circuit 820. In an implementation, eachphotosensor segment 815 ₁-815 _(N) is connected to an input of anoperational amplifier 825. The circuit 800 ensures that, during normaloperation, each photosensor segment 815 ₁-815 _(N) is biased at 0V. Theoutput voltage V_(out) is equal to the negative of the sum of all theindividual photosensor segment 815 ₁-815 _(N) currents, multiplied by afeedback resistance R_(FB). This means that the signals from eachphotosensor segment 815 ₁-815 _(N) is added or averaged, multiplied by aconstant, and inverted to generate the output voltage V_(out). Thebiasing circuit of FIG. 8 is illustrative and other schemes are possiblewithout departing from the scope of the specification and claims herein.

While the emitter segment 150 may reduce its brightness with age (giventhe same input current), the photosensor segment 140 will change itscharacteristics at a much slower rate since no high currents are beingpassed through it. Also, the optical flux and temperature should belower than what the emitter segment 150 is exposed to. As a result, theresponse of the photosensor segment 140 is expected to be more stableover time than the response of the emitter segment 150. The fluxdependence and temperature dependence of the photosensor segment 140 maybe different from that of the emitter segment 150.

As described and illustrated in FIGS. 6-8, the output of the detectorcircuits can be used in a feedback loop using the LED driver. Forinstance, the current output of the driver can be made equal to somenominal value plus an additional current that is inversely proportionalto the sensor current (or proportional to the inverted output of one ofthe inverting sensor circuits). The feedback will adjust the drivecurrent until the light generated reaches the desired value. The amountof light generated (proportional to driver current) can be controlled byadjusting the nominal current, or the degree of feedback. The amount offeedback can be adjusted by adjusting the feedback resistor R_(FB) inFIG. 6-8 or it can be adjusted in the driver circuit.

One advantage of providing this feedback is that the drive current canautomatically be increased as the LED (emitter segment) ages. During LEDaging, the output power changes, usually by decreasing. Providingoptical-based feedback to the LED driver can allow the LED driver tocompensate, keeping the light output constant over the lifetime of thedevice. The LED can maintain a very constant light output for arelatively long time. Depending on the amount that the LED driveradjusts the output, the LED driver may stop increasing the current atsome point. After this point is reached, the LED light output wouldstart decreasing with time. On the other hand, if the LED driver neverstops increasing the current to compensate for the aging of the LED, theLED will maintain a constant light output until it failscatastrophically. This may be a benefit since the catastrophic failurewill signal the user to replace the unit.

Since the LED light output remains constant for a long period, the LEDmay be driven harder and closer to the drive current failure limit. Morelight will be generated from a single LED, and the cost per unit opticalflux will be reduced. Similarly, the LED can be driven at a hottertemperature, closer to the temperature failure limit, reducing the costof the heat sink.

For the case of the ultimate low-cost light source, this feedback canallow the LED to operate at a high temperature and high current density.This reduces the cost of the heat sink and reduces the number of LEDsrequired. The LED will operate at a constant light output until acatastrophic failure.

This method of providing feedback should be useful in many applications,such as automotive, direct colors, and illumination where the failuremode is flux degradation.

If the photosensor output current can be made relatively independent oftemperature, then this feedback can also stabilize the LED output overchanges in operating temperature.

It is also possible to integrate the signal from the photosensor segmentfor some period of time, equivalent to integrating the light output ofthe emitter segment. This can give information about the dose of light.For example, the emitter segment can remain on until a certain number ofphotons have been collected, and then a signal is sent to the LED driverto turn the emitter segment off. This might find an application in LEDsfor camera flash applications. For examples of integrating circuits thatbias a sensor and read-out the integrated signal, see chapter 7 of“Fundamentals of Infrared and Visible Detector Operation and Testing” byJohn David Vincent, John Vampola, Greg Pierce, Steve Hodges, MarkStegall, the contents of which are incorporated herein.

The photosensor segment 150 can be used to send a signal if apre-determined amount of flux is not being generated in the emittersegment 140. For example, the output can be made to be negative duringnormal operation and positive when there is a fault. It is also possibleto make the output close to 0V or some reference voltage during normaloperation and some other voltage when there is a fault.

FIG. 9 is an illustrative schematic of a circuit 900 in accordance withcertain implementations. The circuit 900 includes an emitter segment905, a photosensor segment 910 and a detector circuit 915 that isconnected to the photosensor segment 910. The detector circuit 915includes an operational amplifier 920 connected to a voltage source 925at a positive input terminal and connected to a resistor RFD at anegative input terminal. The detector circuit 915 provides a negativevoltage output when the emitter segment 905 is operating normally, withenough flux and provides a positive voltage when there is a fault (i.e.,not enough flux is being generated by the emitter segment 905). Theresistor R_(FD), V_(REF), and V1 are chosen to adjust the minimumacceptable sensor current I_(S)(min)=(V_(REF)−V1)/R_(FD). V1 is avoltage used to bias resistor R_(FD). V1 should be less than V_(REF)plus the sensor open-circuit voltage and can be set to 0V, −V, orV_(REF).

FIG. 10 is an illustrative schematic of a circuit 1000 in accordancewith certain implementations. The circuit 1000 includes an emittersegment 1005, a photosensor segment 1010 and a detector circuit 1015that is connected to the photosensor segment 1010. The detector circuit1015 includes an operational amplifier 1020 connected to a voltagesource 1025 at a positive input terminal and connected to a resistorR_(FD) at a negative input terminal. A feedback diode 1030 is connectedbetween an output of the operational amplifier 1020 and the negativeinput terminal of the operational amplifier 1020. The detector circuit1015 provides, during normal operation, an output voltage, V_(out),equal to the reference voltage V_(REF) minus the turn-on voltage of thefeedback diode 1020, V_(FD). During a fault, V_(out) is close to thepositive rail voltage. In this implementation, the photosensor segment1010 is biased at 0V during normal operation. These circuits areillustrative and other circuits are envisioned without departing fromthe scope of the specification and claims herein.

FIG. 11 is an illustrative cross-sectional view of a LED die 1100implemented in a flip-chip configuration, where all of the electrodesare on the bottom. In another implementation, a LED die can have one ormore electrodes on top and use wire bonds to create the electricalconnections. The LED die 1100 is formed of semiconductor epitaxiallayers, including an n-type layer 1105, an active layer 1107, and ap-type layer 1109, grown on a growth substrate 1110. In a non-limitingillustrative example, the semiconductor epitaxial layers are made fromgallium nitride (GaN), the active layer 1107 emits blue light and thegrowth substrate 1110 is a transparent sapphire substrate. The growthsubstrate 110 may remain or be removed, such as by laser lift-off,etching, grinding, or by other techniques. The growth processes areformed on a wafer scale and the LED dies are then singulated from thewafer. A phosphor layer (not shown) may overlie the growth substrate1110 for converting the blue primary light to white light or any othercolor light.

A metal electrode 1119 electrically contacts the p-type layer 1109, anda metal electrode 1115 electrically contacts the n-type layer 1105 via avertical conductor 1117 through the p-type layer 1109 and the activelayer 1107. A thin dielectric (not shown) insulates the verticalconductor 1117 from the p-type layer 1109 and the active layer 1107. Adielectric layer 1120 insulates the metal electrode 1115 from the p-typelayer 1109. In a non-limiting illustrative example, the electrodes 1119and 1115 are gold pads that are ultrasonically welded to anode andcathode metal pads 1129 and 1125 on a ceramic submount 1130 or a printedcircuit board. In an implementation, the ceramic submount 1130 may haveconductive vias (not shown) leading to bottom metal pads for bonding toa printed circuit board.

During wafer processing of the LED dies 1100, a surface is patterned andetched, using conventional techniques, to form a trench 1135, whichelectrically isolates a dual purpose segment 1140 from an emittersegment 1150. The dual purpose segment 1140 functions as an embeddedsensor and as an emitter in LED dies 1100. In an implementation, thetrench 1135 may be filled with a transparent material to improve theoptical coupling between the emitter segment 1150 and the dual purposesegment 1140. The dual purpose segment 1140 has the exact same layers asthe emitter segment 1150 and has a vertical conductor 1117 connectingits n-type layer 1105 to a dual purpose electrode 1145. The p-type layer1109 of the dual purpose segment 1140 is connected to a dual purposeelectrode 1149. The trench 1135 surrounds the dual purpose segment 1140for complete electrical insulation. In an implementation, electricalisolation may be provided by injection of certain types of atoms aroundthe dual purpose segment 1140, which causes the GaN material surroundingthe dual purpose segment 1140 to be effectively an insulator.

The dual purpose electrodes 1145 and 1149 are connected to contact pads1155 and 1159 on the submount 1130 or printed circuit board forconnection to a detector circuit 1180 (details shown in FIGS. 4-10). Inan implementation, there are four electrodes on the LED die 1100 toallow the emitter segment 1150 and the photosensor segment 1140 to beconnected completely independently.

In an implementation, the dual purpose segment 1140 is switched betweenoperating as a photosensor or as an emitter on a periodic basis. In animplementation, the dual purpose segment 1140 is switched betweenoperating as a photosensor or as an emitter on an on-demand basis. In animplementation, a controller 1190 can operate dual purpose segment 1140as a photosensor as described herein or as an emitter such as emittersegment 1150. The controller 1190 can be connected to the dual purposesegment 1140 via the submount 1130 and the dual purpose electrodes 1145and 1149 and contact pads 1155 and 1159.

Operationally, when the dual purpose segment 1140 is operating as aphotosensor, side light 1160 emitted by the emitter segment 1150impinges on the active layer 1107 within the dual purpose segment 1140and is converted into a small current in a direction opposite to theemitter segment 1150 current. The current is the product of the photonsexciting the electrons in the dual purpose segment's 1140 active layer1107. Since the dual purpose segment 1140 and the emitter segment 1150have the same active layer 1107, only the narrow wavelength of lightemitted by emitter segment 1150 is converted into a small current by thedual purpose segment 1140. This is beneficial since ambient light willhave little effect on the output of the dual purpose segment 1140.Further, since the dual purpose segment 1140 very close to the emittersegment 1150, there is little light attenuation in the gap. Accordingly,the system is very efficient, reproducible, and accurate. The verticalconductor 1117 is preferably located away from the emitter segment 1150to not attenuate the light. A blue light ray 1165 exiting the top of theemitter segment 1150 may be converted by a phosphor layer to any othercolor. Such a phosphor layer does not affect the operation of the dualpurpose segment 1140. When the dual purpose segment 1140 is operating asan emitter, a blue light ray 1167 exiting the top of the dual purposesegment 1140 may be converted by a phosphor layer to any other color.

FIG. 12 is an illustrative cross-sectional view of a LED die 1200implemented in a flip-chip configuration, where all of the electrodesare on the bottom. In another implementation, a LED die can have one ormore electrodes on top and use wire bonds to create the electricalconnections. The LED die 1200 is formed of semiconductor epitaxiallayers, including an n-type layer 1205, an active layer 1207, and ap-type layer 1209, grown on a growth substrate 1210. In a non-limitingillustrative example, the semiconductor epitaxial layers are made fromgallium nitride (GaN), the active layer 1207 emits blue light and thegrowth substrate 1210 is a transparent sapphire substrate. The growthsubstrate 1210 may remain or be removed, such as by laser lift-off,etching, grinding, or by other techniques. The growth processes areformed on a wafer scale and the LED dies are then singulated from thewafer. A phosphor layer (not shown) may overlie the growth substrate1210 for converting the blue primary light to white light or any othercolor light.

A metal electrode 1219 electrically contacts the p-type layer 1209, anda metal electrode 1215 electrically contacts the n-type layer 1205 via avertical conductor 1217 through the p-type layer 1209 and the activelayer 1207. A thin dielectric (not shown) insulates the verticalconductor 1217 from the p-type layer 1209 and the active layer 1207. Adielectric layer 1220 insulates the metal electrode 1215 from the p-typelayer 1209. In a non-limiting illustrative example, the electrodes 1219and 1215 are gold pads that are ultrasonically welded to anode andcathode metal pads 1229 and 1225 on a ceramic submount 1230 or a printedcircuit board. In an implementation, the ceramic submount 1230 may haveconductive vias (not shown) leading to bottom metal pads for bonding toa printed circuit board.

During wafer processing of the LED dies 1200, a segmentation layer 1235electrically and optically isolates and/or insulates a photosensorsegment 1240 from an emitter segment 1250. In an implementation, thesegmentation layer 1235 electrically and optically isolates and/orinsulates the photosensor segment 1240 from the emitter segment 1250 tomaximize light output. In an implementation, additional layers may beadded in conjunction with the segmentation layer 1235 to focus or directlight rays out of the emitter segment 150. In an implementation, thesegmentation layer 1235 is an oxide layer that is deposited usingconventional techniques including, for example, patterning a surface,masking and depositing a given material as is known in the art. In animplementation, the segmentation layer 1235 is formed by ionimplantation. The photosensor segment 1240 functions as an embeddedsensor in LED dies 1200. The photosensor segment 1240 has the exact samelayers as the emitter segment 1250 and has a vertical conductor 1217connecting its n-type layer 1205 to a photosensor electrode 1245. Thep-type layer 1209 of the photosensor segment 1240 is connected to aphotosensor electrode 1249. In an implementation, the photosensorsegment 1240 will typically have an area that is less than 10% of theemitter segment 1250. In an implementation, the photosensor segment 1240may be a small portion along one edge of the emitter segment 1250. Inanother implementation, the photosensor segment 1240 may be surroundedby the emitter segment 1250. In another implementation, the photosensorsegment 1240 may take up an entire edge of the LED die 1200.

Operationally, a blue light ray 1265, for example, is emitted from thetop of the emitter segment 1250 into the growth substrate 1210. Totallyinternally reflected and Fresnel reflected light rays 1267 are reflectedback to the photosensor segment 1240 and are converted into a current ina direction opposite to the emitter segment 1250 current. The current isthe product of the photons exciting the electrons in the photosensorsegment's 1240 active layer 1207. Since the photosensor segment 1240 andthe emitter segment 1250 have the same active layer 1207, only thenarrow wavelength of light emitted by emitter segment 1250 is convertedinto the current by the photosensor segment 1240. This is beneficialsince ambient light will have little effect on the output of thephotosensor segment 1240. The vertical conductor 1217 is preferablylocated away from the emitter segment 1250 to not attenuate the light.The blue light ray 1265 exiting the top of the emitter segment 1250 maybe converted by a phosphor layer to any other color. Such a phosphorlayer does not affect the operation of the photosensor segment 1240.

The photosensor electrodes 1245 and 1249 contact pads 1255 and 1259 onthe submount 1230 or printed circuit board for connection to a detectorcircuit (shown in FIGS. 4-10). In an implementation, there are fourelectrodes on the LED die 1200 to allow the emitter segment 1250 and thephotosensor segment 1240 to be connected completely independently.

Each of the implementations described herein can be used with thetechniques of other implementations. For example, the implementation ofFIG. 11 can be implemented with the insulation layer described in FIG.12.

In an implementation, a LED die can be segmented into multiple segments,where one segment functions as a photosensor. In this implementation,the segment functioning as a photosensor used to sense the performancefor all emitter segments. In an implementation, each segment could emita different color. In an implementation, a red emitting emitter segmentacts as the photosensor as the red emitting emitter segment has thesmallest bandgap.

For the implementations described herein, normally, when LEDs areconnected in series, fault detection is done by comparing the LED stringvoltage to an expectation. However, many voltage sensing circuits assumethat the fault is a short circuit or assume that the fault is an opencircuit. Also, voltage-sensing fault detection circuits are affected bychanges in the LED voltage that occur over the lifetime of the device.The present invention results in an optical-based fault detection orfeedback. It is the light that is being sensed, not the voltage. Thisoptical-based fault detection scheme does not require an assumption thatthe failure will be an open or a short. Also, it is not affected bychanges to the operating voltage over the lifetime of the device.

With the sensor diode electrodes being separate from the LED electrodes,it is also possible to wire the LED and the sensor together. If they arewired in parallel, then the sensor diode generates light, along with theLED, making the device more efficient. When they are wiredanti-parallel, the sensor diode acts like a transient voltagesuppression diode. One advantage of having the LED and sensor electrodesbeing separate on the die is that the connection configuration happensnot on the LED chip, but on the submount or printed circuit board.Different submount configurations can result in the parallel connectionfor higher efficiency, anti-parallel configuration for transient voltagesuppression, or independently wired for use as an LED and sensor.

In another embodiment, the sensor is a separately formed die that issmaller than the LED die, but having the same semiconductor layers. Thesensor chip is mounted in the same package as the LED chip to maintain apredetermined positional relationship. The package then has the fourelectrodes, such as shown in FIG. 2 or 3.

FIG. 13 is a flowchart for making a light emitting device in accordancewith certain implementations. A light emitting diode (LED) die is formedby growing a semiconductor stack on a substrate, where the semiconductorstack includes an n-type layer, an active layer and a p-type layer(1305). An isolation configuration is formed during the growth of thesemiconductor stack to electrically isolate segments of thesemiconductor stack (1310). In an implementation, the isolationconfiguration optically isolates the segments. In an implementation, theisolation configuration is a trench. In an implementation, the isolationconfiguration is an insulation barrier implemented via ion implantationor an oxidation process. An emitter segment is formed from one segmentconfigured to emit a first light ray (1315). A dual purpose segment isformed from another segment to operate in a first mode to sense a secondlight ray and generate a current responsive to the second light ray andconfigured to operate in a second mode to emit a third light ray, thedual purpose segment configured to switch between the first mode and thesecond on a given basis (1320). First electrodes are connected to theemitter segment to provide power to energize the emitter segment (1325).Second electrodes are connected to the dual purpose segment, the secondelectrodes configured to operate in the first mode to send the currentto a detector, the detector circuit configured to convert the current toa signal which provides operational feedback with respect to the emittersegment, and the second electrodes configured to operate in the secondmode to provide power to energize the dual purpose segment to emit thethird light ray (1330).

The embodiments described herein may be incorporated into any suitablelight emitting device. Embodiments of the invention are not limited tothe particular structures illustrated, such as, for example, the devicesof FIGS. 1-13.

Though in the examples and embodiments described above the semiconductorlight emitting device is a III-nitride LED that emits blue or UV light,semiconductor light emitting devices besides LEDs, such as laser diodes,are within the scope of the invention. In addition, the principlesdescribed herein may be applicable to semiconductor light emittingdevices made from other materials systems such as other III-V materials,III-phosphide, III-arsenide, II-VI materials, ZnO, or Si-basedmaterials.

The non-limiting methods described herein for light emitting diodes withsensor segments for operational feedback may be modified for a varietyof applications and uses while remaining within the spirit and scope ofthe claims. The implementations and variations described herein, and/orshown in the drawings, are presented by way of example only and are notlimiting as to the scope and spirit. The descriptions herein may beapplicable to all implementations of the method for using and makinglight emitting diodes with sensor segments for operational feedbackalthough it may be described with respect to a particularimplementation.

As described herein, the methods described herein are not limited to anyparticular element(s) that perform(s) any particular function(s) andsome steps of the methods presented need not necessarily occur in theorder shown. For example, in some cases two or more method steps mayoccur in a different order or simultaneously. In addition, some steps ofthe described methods may be optional (even if not explicitly stated tobe optional) and, therefore, may be omitted. These and other variationsof the methods disclosed herein will be readily apparent, especially inview of the description of the method for using and making lightemitting diodes with sensor segments for operational feedback asdescribed herein, and are considered to be within the full scope of theinvention.

Some features of some implementations may be omitted or implemented withother implementations. The device elements and method elements describedherein may be interchangeable and used in or omitted from any of theexamples or implementations described herein.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements.

What is claimed is:
 1. A light emitting device comprising: an emittersegment a first semiconductor stack comprising an n-type material, ap-type material, and an active material between the n-type material andthe p-type material; a sensor segment electrically isolated from theemitter segment and including a second semiconductor stack of an n-typematerial, a p-type material, and an active material between the n-typematerial and the p-type material; a transparent substrate disposed overboth the emitter segment and the sensor segment; and first and secondelectrodes disposed on the emitter segment.
 2. The device of claim 1,further comprising a trench between the first and the secondsemiconductor stacks.
 3. The device of claim 2, further comprising atransparent material in the trench.
 4. The device of claim 1, furthercomprising a first via formed through the active material and one of thep-type material and the n-type material of the emitter segment, thefirst via lined with an electrically insulating material and filled withan electrically conductive material.
 5. The device of claim 1, furthercomprising a second via formed through the active material and one ofthe p-type material and the n-type material of the sensor portion, thesecond via lined with an electrically insulating material and filledwith an electrically conductive material.
 6. The device of claim 1,wherein the transparent substrate has a second surface facing away fromthe n-type material and opposite a first surface, and is configured toprovide total internal reflection of some amount of light incident onthe second surface.
 7. The device of claim 1, wherein the electricalinsulating material completely surrounds the sensor segment.
 8. A lightemitting diode (LED) device system comprising: a light emitting elementcomprising: a semiconductor stack comprising an n-type material, ap-type layer, and an active material between the n-type material and thep-type material; an electrical isolation region electrically isolatingthe semiconductor stack into a first segment and a second segment; adriver circuit electrically coupled to the first segmentportion andconfigured to provide a drive current to drive the first segment as anemitter; and a bias circuit electrically coupled to operate the secondsegment as a sensor segment and provide an input current to the drivercircuit based on an amount of light impinging on the second segment. 9.The system of claim 8, further comprising a transparent substratedisposed over both the first segment and the second segment.
 10. Thesystem of claim 9, further comprising: at least one anode electrodedisposed on the light emitting element; and at least one cathodeelectrode disposed on the light emitting element, wherein each of thefirst segment and the second segment are electrically coupled to one ofthe at least one cathode electrode and one of the at least one anodeelectrode.
 11. The system of claim 9, wherein the transparent substratehas a second surface opposite a first surface and is configured toprovide total internal reflection of light incident on the secondsurface of the transparent substrate.
 12. The system of claim 8, whereinthe electrical isolation region comprises one of a trench and aninsulating region of semiconductor material in the semiconductor stack.13. The system of claim 8, further comprising a controller configured toperform at least one of: periodically switching the second segmentbetween operation as an emitter and operation as a sensor, or switchingthe second segment between operation as an emitter and operation as asensor in response to a control signal.
 14. The system of claim 8,wherein the bias circuit is configured to bias the second segment toprovide a positive voltage on a condition that light emitted by thefirst segment is below a threshold and provide a negative voltage on acondition that light emitted by the first segment is above thethreshold.
 15. The system of claim 8, wherein the input current to thedriver circuit adjusts the drive current higher on a condition thatlight emitted by the first segment is below a threshold.
 16. A method ofmanufacturing a light emitting diode (LED) device, the methodcomprising: growing an n-type material, a p-type material, and an activematerial on a substrate to form a semiconductor stack on the substrate;etching a trench through the p-type material, the n-type material, andthe active material to divide the semiconductor stack into an emittersegment and a sensor segment; electrically coupling a respective firstelectrode directly to one of the p-type material and the n-type materialof the emitter segment and the sensor segment; forming a separate viathrough each of the emitter segment and the sensor segment; andelectrically coupling a respective second electrode to the other one ofthe p-type material and the n-type material through each separate via.17. The method of claim 16, further comprising filling the trench with atransparent material.